The accessory olfactory bulb (AOB) is the first relay of chemosensory information in the vomeronasal system, yet very few studies have addressed cell physiology and synaptic connectivity of cells in the AOB. Principal neurons in the AOB, unlike cells in the main olfactory bulb (MOB), send primary dendrites to more than one glomerulus, and peripheral sensory neurons expressing a single vomeronasal receptor (VR) in the vomeronasal organ (VNO) project to multiple glomeruli. There is also a segregation of projections from sensory neurons in the VNO into the anterior and posterior aspects of the AOB, and this segregation may also result in differential patterns of activity in these regions. The overall aim of this application is to study the physiological properties of principal neurons in the AOB. We will relate physiological characteristics to anatomical parameters of the cells, particularly glomerular connectivity, and their distribution in the anterior-posterior axis of the AOB. In Specific Aim 1, we will determine if mitral cells are connected only to glomeruli that receive inputs from the same receptor, or if the same mitral cell maintains connection with a mixed population of receptors. We will use two lines of transgenic mice, the V1r and V2r-GFP mice. Recording from mitral cells connected to GFP-labeled glomeruli and including a fluorescent dye in the intracellular recording solution will allow identification of the cell's glomerular connection(s). We will compare the number of GFP-labeled glomeruli with those labeled by the intracellular dye. In Specific Aim 2, we will study the pharmacological and physiological properties of dendrodendritic inhibition in mitral cells. Because VNO neurons expressing the V1r and V2r project to the anterior and posterior AOB respectively, the use of these transgenic mice will allow us to compare these subdivisions of the AOB. It is anticipated that these studies will have an impact on our understanding of the sensory coding of pheromonal information and other olfactory information by the accessory olfactory system.